Upgrade to the RTM Bits for SQL Server 2005
Like Silk. I had an instance of the full imprint of SQL Server 2000 SP4 (Database Engine, Analysis Services, Reporting Services, etc.). I just ran through the setup and it worked wonderfully. It detected the installed products and versions and asked me what I wanted to do with them. When attempting to upgrade, select the SQL Server 2005 instance as the default instance. It notices that you already have a default instance and will prompt to upgrade it. Next, I'm going to try it on my Virtual Machine which has a the August CTP bits.